Transmitter, transmission method, receiver, and reception method

ABSTRACT

An association with a system timing at the time of transmission is secured without changing a display timing in text information of a subtitle, and a reception side displays the subtitle at an appropriate timing. 
     A packet in which a document of the text information of the subtitle having display timing information is included in a payload is generated and transmitted in synchronization with a sample period. A header of the packet includes a time stamp on a first time axis indicating a start time of the corresponding sample period. The payload of the packet further includes reference time information of a second time axis regarding the display timing associated with the start time of the corresponding sample period.

TECHNICAL FIELD

The present technology relates to a transmitter, a transmission method,a receiver, and a reception method, and more particularly, to atransmitter and the like for transmitting a document of text informationof a subtitle having display timing information.

BACKGROUND ART

Conventionally, for example, in broadcasting with Digital VideoBroadcasting (DVB) and the like, and an operation for transmittinginformation of a subtitle as bit map data is performed. Recently, it hasbeen suggested to transmit subtitle information in a text charactercode, that is, in a text-based way. In this case, a font is expandedaccording to a resolution by a reception side.

Furthermore, in a case where the subtitle information is transmitted ina text-based way, it has been proposed that the text informationincludes timing information. As the text information, for example, theWorld Wide Web Consortium (W3C) proposes the Timed Text Markup Language(TTML) (refer to Patent Document 1).

CITATION LIST Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2012-169885

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

It is considered that a packet including a document of the TTML isgenerated and transmitted in synchronization with a sample period (fixedsection). In this case, a header of the packet includes a time stampindicating a start time of the corresponding sample period. Regardingthe time stamps, timings are uniformly managed in a whole system.

A display timing (begin, end) of a domain of the TTML is only a relativetiming of each TTML package, and the display timing does not synchronizewith a system. On the other hand, a subtitle of the TTML is produced foreach content and is independent from timing management at the time ofdistribution. Therefore, a synchronization method is required thatsecures an association with a system timing at the time of transmissionwithout changing the display timing (begin, end) which is a relativetiming of the subtitle of the TTML.

An object of the present technology is to secure an association with asystem timing at the time of transmission without changing a displaytiming in text information of a subtitle and display the subtitle at anappropriate timing by a reception side.

Solutions to Problems

A concept of the present technology is

a transmitter including

a packet transmission unit that generates and transmits a packet inwhich a document of text information of a subtitle having display timinginformation is included in a payload in synchronization with a sampleperiod, in which

a time stamp on a first time axis indicating a start time of thecorresponding sample period is included in a header of the packet, and

the payload of the packet further includes reference time information ofa second time axis regarding the display timing, associated with thestart time of the corresponding sample period.

In the present technology, the packet is generated and transmitted bythe transmission unit in synchronization with the sample period. Thepayload of the packet includes the document of the text information ofthe subtitle having the display timing information. For example, thepacket may be a PES packet. Furthermore, the text information of thesubtitle may be described in the TTML or a format derived from the TTML.

The header of the packet includes the time stamp on the first time axisindicating the start time of the corresponding sample period.Furthermore, the payload of the packet further includes the referencetime information of the second time axis regarding the display timing,associated with the start time of the corresponding sample period. Forexample, the reference time information may be time informationindicating the start time of the corresponding sample period.Furthermore, for example, the reference time information may be timeinformation indicating a difference between the display start timeindicated by the display timing information and the start time of thecorresponding sample period or a difference between the display end timeindicated by the display timing information and the start time of thecorresponding sample period. Furthermore, for example, a time may beindicated by a count value of 90 kHz on the first time axis, and a timemay be indicated by an hour-minute-second frame on the second time axis.

Furthermore, for example, the payload of the packet may include a firstsegment having the document of the text information of the subtitle anda second segment having the reference time information regarding thedisplay timing. Then, in this case, the first segment may be associatedwith the second segment corresponding to the first segment withidentification information.

As described above, in the present technology, the header of the packetincludes the time stamp on the first time axis indicating the start timeof the corresponding sample period, and the payload of the packetincludes the reference time information of the second time axisregarding the display timing, associated with the start time of thecorresponding sample period. Therefore, it is possible to secure anassociation with the system timing at the time of transmission withoutchanging the display timing in the text information of the subtitle, andthe reception side can display the subtitle at an appropriate timing.

Note that, in the present technology, for example, the packettransmission unit may generate and transmit the packet in the sampleperiod after the display start time indicated by the display timinginformation has passed. This enables to increase a display probabilityof the subtitle at the time of random access caused by channelswitching, for example.

Furthermore, another concept of the present technology is

a receiver including

a reception unit that receives a packet in which a document of textinformation of a subtitle having display timing information is includedin a payload in synchronization with a sample period, in which

a time stamp on a first time axis indicating a start time of thecorresponding sample period is included in a header of the packet, and

the payload of the packet further includes reference time information ofa second time axis regarding the display timing, associated with thestart time of the corresponding sample period, and

the receiver further includes a control unit that controls a displaytiming of the subtitle according to the text information of the subtitleon the basis of the time stamp and the reference time information.

In the present technology, the reception unit receives the packet inwhich the document of the text information of the subtitle having thedisplay timing information is included in the payload in synchronizationwith the sample period. Here, the header of the packet includes the timestamp on the first time axis indicating the start time of thecorresponding sample period. Furthermore, the payload of the packetfurther includes the reference time information of the second time axisregarding the display timing, associated with the start time of thecorresponding sample period.

The control unit controls the display timing of the subtitle accordingto the text information of the subtitle on the basis of the time stampand the reference time information. For example, the control unit mayconvert the display start time and the display end time indicated by thedisplay timing information to a time on the first time axis by using thetime stamp and the reference time information and control the displaytiming of the subtitle by using the converted time. Furthermore, forexample, the control unit may perform control to immediately display thesubtitle according to the text information of the subtitle when thedisplay start time indicated by the display timing information ispositioned previously.

In this way, in the present technology, the header of the packetincludes the time stamp on the first time axis indicating the start timeof the corresponding sample period, the payload of the packet includesthe reference time information of the second time axis regarding thedisplay timing, associated with the start time of the correspondingsample period, and the display timing of the subtitle according to thetext information of the subtitle is controlled on the basis of the timestamp and the reference time information. Therefore, it is possible todisplay the subtitle at an appropriate timing.

Note that, in the present technology, for example, it is possible thatthe payload of the packet includes a first segment having the documentof the text information of the subtitle and a second segment having thereference time information regarding the display timing, the firstsegment is associated with the second segment corresponding to the firstsegment with identification information, and the control unit controlsthe display timing of the subtitle according to the text information ofthe subtitle included in the first segment by using the reference timeinformation included in the second segment associated with the firstsegment. With this control, it is possible to avoid that the displaytiming is controlled by using wrong reference time information.

Effects of the Invention

According to the present technology, it is possible to secure anassociation with a system timing at the time of transmission withoutchanging a display timing in text information of a subtitle, and areception side can display the subtitle at an appropriate timing. Notethat the effects described herein are only exemplary and not limited tothese. Furthermore, there may be an additional effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an exemplary configuration of atransmission/reception system according to an embodiment.

FIG. 2 is a block diagram of an exemplary configuration of a streamgeneration unit of a broadcast transmission system.

FIG. 3 is a diagram to describe a TTML structure.

FIG. 4 is a diagram of an exemplary structure of each element ofmetadata, styling, and layout existing in a header (head) of the TTMLstructure.

FIG. 5 is a diagram of an exemplary structure of a body of the TTMLstructure.

FIG. 6 is a diagram of an exemplary generation timing of a subtitle PESpacket.

FIG. 7 is a diagram to describe reference time information.

FIG. 8 is a schematic diagram of an exemplary content (packet structure)of the subtitle PES packet.

FIG. 9 is a schematic diagram of an exemplary content of a subtitle PESpacket in a case of rebroadcasting.

FIG. 10 is a schematic diagram of an exemplary content (packetstructure) of the subtitle PES packet.

FIG. 11 is a diagram of an example of two subtitle contents which havebeen individually produced.

FIG. 12 is a schematic diagram of an exemplary content (packetstructure) of a subtitle PES packet in a case where subtitle contents S1and S2 exist.

FIG. 13 is a diagram of an exemplary arrangement sequence in a casewhere TTLM documents and reference time segments regarding the subtitlecontents S1 and S2 exist in the subtitle PES packet.

FIG. 14 is a diagram of an exemplary structure of the subtitle PESpacket.

FIG. 15 is a diagram of an exemplary structure of the subtitle PESpacket (PES_packet) and an exemplary structure of “PES_data_byte_field()”.

FIG. 16 is a diagram of an exemplary definition of a TT subtitle segmenttype.

FIG. 17 is a diagram of an exemplary structure of a TTML segment and acontent of main information in the exemplary structure and the like.

FIG. 18 is a diagram of an exemplary structure of the reference timesegment and a content of main information in the exemplary structure andthe like.

FIG. 19 is a block diagram of an exemplary configuration of a televisionreceiver.

FIG. 20 is a diagram of an exemplary processing procedure of subtitledisplay control performed each time when a CPU receives the subtitle PESpacket.

MODE FOR CARRYING OUT THE INVENTION

A mode for carrying out the present invention (referred to as“embodiment”) will be described below. Note that the description will bemade in the following order.

1. Embodiment

2. Modification

1. Embodiment

[Exemplary Configuration of Transmission/Reception System]

FIG. 1 is an exemplary configuration of a transmission/reception system10 as an embodiment. The transmission/reception system 10 includes abroadcasting transmission system 100 and a television receiver 200.

The broadcasting transmission system 100 transmits an MPEG-2 transportstream (hereinafter simply referred to as “transport stream”) TS as amultiplexed stream on a broadcast wave.

The transport stream TS has a subtitle stream together with a videostream and an audio stream. The video stream includes a video PES packetin which encoded image data is arranged in a payload. The audio streamincludes an audio PES packet in which encoded audio data is arranged ina payload.

The subtitle stream includes a subtitle PES packet in which a documentof text information of a subtitle having display timing information thatis a segment packet having a TTML document (TTML document) in theembodiment is arranged in a payload. The subtitle PES packet isgenerated in synchronization with a sample period (fixed section).

A header of the subtitle PES packet includes a time stamp on a firsttime axis indicating a start time of the corresponding sample period.The time stamp is a so-called Presentation Time Stamp (PTS), and a timeis indicated with a count value of 90 kHz. In this case, the PTSconfigures a sample start time. Regarding the PTS, timings are uniformlymanaged in the whole system.

Furthermore, the payload of the subtitle PES packet includes referencetime information of a second time axis regarding a display timing(begin, end), associated with the start time of the corresponding sampleperiod. The display timing (begin, end) is only a relative timing foreach package of the TTML. The display timing is not synchronized withthe system and is independent from timing management at the time ofdistribution. In the present embodiment, the reference time informationis time information indicating the start time of the correspondingsample period, and in the reference time information, a time isindicated by an hour-minute-second frame.

The payload of the subtitle PES packet includes a first segment(TTML_segment) having the document of the text information of thesubtitle described above and a second segment (Reftime_segment) havingthe reference time information regarding the display timing describedabove. Here, the first segment and the second segment corresponding tothe first segment form a single pair (group), and the segments have thesame identification information and are associated with each other. In acase where a plurality of subtitle contents which has been individuallyproduced exists, the payload of the subtitle PES packet may include aplurality of pairs (group) of the first segments and the secondsegments. However, the pairs can be identified from each other with theidentification information.

The television receiver 200 receives the transport stream TS transmittedon the broadcast wave from the broadcasting transmission system 100. Asdescribed above, the transport stream TS includes the subtitle streamtogether with the video stream and the audio stream. As described above,the subtitle stream is configured of the subtitle PES packet. Thesubtitle PES packet includes the first segment (TTML_segment) having thedocument of the text information of the subtitle and the second segment(Reftime_segment) having the reference time information regarding thedisplay timing.

The television receiver 200 controls a timing to display the subtitleaccording to the text information of the subtitle on the basis of thetime stamp and the reference time information. As described above, thetime stamp is time information regarding the first time axis, and thereference time information is time information regarding the second timeaxis similarly to the display timing information included in the TTML.The television receiver 200 converts a display start time and a displayend time indicated by the display timing information into a time on thefirst time axis and controls a subtitle display timing by using theconverted time.

Here, the first segment and the second segment corresponding to thefirst segment form a single pair (group), and the segments have the sameidentification information and are associated with each other. Thetelevision receiver 200 controls the subtitle display timing accordingto the text information of the subtitle included in the first segment byusing the reference time information included in the second segmentwhich is associated with the first segment.

Note that to increase a display probability of the subtitle at the timeof random access caused by channel switching, the subtitle PES packetsincluding the same TTML document may be sequentially transmitted insynchronization with a plurality of sample periods. In that case, ineach subtitle PES packet, times indicated by the reference timeinformation included in the subtitle PES packets sequentially change asthe corresponding sample period advances. In this case, the subtitle PESpacket is generated and transmitted in a sample period after the displaystart time indicated by the display timing information has passed. Whenthe display start time indicated by the display timing information isset before the start time of the sample period, a receiver 200 performscontrol to immediately display the subtitle.

[Exemplary Configuration of Stream Generation Unit of BroadcastTransmission System]

FIG. 2 is an exemplary configuration of a stream generation unit 110 ofthe broadcasting transmission system 100. The stream generation unit 110includes a control unit 111, a video encoder 112, an audio encoder 113,a text format conversion unit 114, a subtitle encoder 115, and a TSformatter (multiplexer) 116.

The control unit 111 includes, for example, a Central Processing Unit(CPU) and controls operations of the units in the stream generation unit110. The video encoder 112 receives image data DV, encodes the imagedata DV, and generates a video stream (PES stream) including the videoPES packet having the encoded image data in the payload. The audioencoder 113 receives audio data DA, encodes the audio data DA, andgenerates an audio stream (PES stream) including the audio PES packethaving the encoded audio data.

The text format conversion unit 114 receives text data (character code)as subtitle information and data DT including display controlinformation of the text data and obtains text information of thesubtitle in a predetermined format having the display timinginformation. As the text information, for example, it is considered touse the TTML or a format derived from the TTML. In the presentembodiment, the TTML is used.

FIG. 3 is an exemplary structure of a document (file) of the TTML. TheTTML is described on the basis of XML. In the TTML, head (head) and body(body) exist. Furthermore, each element of metadata (metadata), styling(styling), and layout (layout) exists in the head (head).

FIG. 4(a) illustrates an exemplary structure of the metadata (TTM: TTMLMetadata). The metadata includes information regarding a title of themetadata and information regarding a copyright.

FIG. 4(b) illustrates an exemplary structure of the styling (TTS: TTMLStyling). In addition to an identifier (id), the styling includesinformation such as a color (color), a font (fontFamily), a size(fontSize), alignment (textAlign), and the like.

FIG. 4(c) illustrates an exemplary structure of the layout (region: TTMLlayout). In addition to an identifier (id) of a region where thesubtitle is arranged, the layout includes information such as a range(extent), an offset (padding), a background color (backgroundColor),alignment (displayAlign), and the like.

FIG. 5 illustrates an exemplary structure of the body (body). In theexample in FIG. 5, information regarding a subtitle 1 (subtitle 1) isincluded. The display start time and the display end time are described,and the text data is described. For example, regarding the subtitle 1(subtitle 1), a display start timing is “3 s”, a display end timing is“6 s”, and the text data is “I'm going to the station now”.

Returning to FIG. 2, the subtitle encoder 115 generates a TTML segment(TTML_segment) including a TTML document obtained by the text formatconversion unit 114. Then, the subtitle encoder 115 generates a subtitlestream (PES stream) including a subtitle PES packet in which the TTMLsegment is arranged in the payload.

The subtitle encoder 115 generates the subtitle PES packet insynchronization with the sample period and inserts the time stamp on thefirst time axis indicating the start time of the corresponding sampleperiod to the header of the subtitle PES packet as a PTS. On the firsttime axis, a time is indicated by a count value of 90 kHz.

FIG. 6 illustrates an exemplary generation timing of the subtitle PESpacket. In FIG. 6, a vertical line indicates a boundary between thesample periods (fixed section). In this example, in synchronization witha certain sample period, a subtitle PES packet having a time stamp A(Timestamp A) indicating a start time of the sample period as a PTS isgenerated. The payload of the subtitle PES packet includes a TTMLsegment (TTML_segment) having a TTLM document having display timinginformation in which a display start time is “J” and a display end timeis “K”.

Furthermore, in this example, in synchronization with a certain sampleperiod, a subtitle PES packet having a time time stamp B (Timestamp B)indicating a start time of the sample period as a PTS is generated. Thepayload of the subtitle PES packet includes a TTML segment(TTML_segment) having a TTLM document having display timing informationin which a display start time is “P” and a display end time is “R”.

Furthermore, the subtitle encoder 115 generates a reference time segment(Reftime_segment) having reference time information of the second timeaxis regarding the display timing which is associated with the starttime of the corresponding sample period, on the basis of timingmanagement by the control unit 111. Then, the subtitle encoder 115includes the reference time segment (Reftime_segment) in the payload ofthe subtitle PES packet. On the second time axis, a time is indicated byan hour-minute-second frame.

With reference to FIG. 7, the reference time information will be furtherdescribed. A time on the first time axis corresponding to the start ofthe sample period is assumed as a “timestamp 1”. Furthermore, thedisplay timing (begin, end) of the subtitle (subtitle) is timeinformation of the second time axis. It is assumed that the displaystart time (begin) be “Time1”, the time on the second time axiscorresponding to the start of the sample period be “Reftime1”, and adifference between “Time1” and “Reftime1” be Δ. In this case, “Reftime1”is the reference time information.

By inserting the reference time information to the payload of thesubtitle PES packet and transmitting the reference time information, areception side can convert the display timing (begin, end) of thesubtitle which is the time information of the second time axis into thefirst time axis and control the display timing of the subtitle by usingthe converted time.

The following formula (1) indicates a conversion formula to obtain“delta90” which is a value of 90 kHz accuracy corresponding to theperiod of Δ. Furthermore, the following formula (2) indicates aconversion formula to obtain “timestamp2” which is a time on the firsttime axis corresponding to the display start time (begin) on the secondtime axis. In addition, the following formula (3) indicates a conversionformula to obtain “Timestamp3” which is a time on the first time axiscorresponding to the display end time (end) of the second time axis.Note that it is assumed that the display end time (end) be “Time1′”.Furthermore, in these formulas, a unit of each of Time1, Reftime1, andTime1′ is “seconds”.delta90=(Time1−Reftime1)*90K  (1)timestamp2=timestamp1+delta90  (2)timestamp3=timestamp2+(Time1′−Time1)*90K  (3)

Note that in the above, a general case where the display start time“Time1” is larger than the time “Reftime1” is described. However, thedisplay start time “Time1” may coincide with the time “Reftime1”. Inthat case, “Reftime1” to be the reference time information is set to“Time1”. In this case, the transmission of the reference timeinformation can be omitted.

FIG. 8 is a schematic diagram of an exemplary content (packet structure)of the subtitle PES packet. This example corresponds to FIG. 6 describedabove. The payload of the subtitle PES packet having the time stamp A(Timestamp A) as the PTS includes the TTML segment (TTML_segment) havingthe TTLM document with the display timing information in which thedisplay start time is “J” and the display end time is “K” and includesthe reference time segment (Reftime_segment) having the reference timeinformation “Reftime1”.

In this case, the reception side can obtain “Ts_Am” which is a time onthe first time axis having 90 kHz accuracy corresponding to the displaystart time (begin) on the second time axis, for example, by thefollowing formula (4).TS_Am=timestampA+(J?Reftime1)*90K  (4)

Furthermore, the payload of the subtitle PES packet having the timestamp B (Timestamp B) as the PTS includes the TTML segment(TTML_segment) having the TTLM document with the display timinginformation in which the display start time is “P” and the display endtime is “R” and includes the reference time segment (Reftime_segment)having the reference time information “Reftime2”. Furthermore, in thiscase, the insertion of the reference time segment (Reftime_segment) canbe omitted.

In this case, the reception side can obtain “Ts_Bm” which is a time onthe first time axis having 90 kHz accuracy corresponding to the displaystart time (begin) on the second time axis, for example, by thefollowing formula (5).TS_Bm=timestampB+(P?Reftime2)*90K=timestampB  (5)

FIG. 9 schematically illustrates an exemplary content of a subtitle PESpacket in a case where the same TTML document is redistributed indifferent broadcasting time zones, for example, in a case ofrebroadcasting. A time stamp of PTS1 is attached at the time of originalbroadcasting, and a time stamp of PTS2 is attached at the time ofrebroadcasting. In the payload, a TTML segment (TTML_segment) having aTTLM document with display timing information in which a display starttime is “00:00:03” and a display end time is “00:00:06” is included atthe times of original broadcasting and rebroadcasting.

Furthermore, in the payload, a reference time segment (Reftime_segment)having “00:00:01” as the reference time information “Reftime1” isincluded at the time of original broadcasting, and a reference timesegment (Reftime_segment) having “00:00:01” as the reference timeinformation “Reftime2” is included at the time of rebroadcasting. Inthis case, a which is a time delay from PTS1 to PTS1_1 which is thedisplay start time is equal to β which is a time delay from PTS2 toPTS2_1 which is the display start time. On the other hand, it ispossible to respectively set different values to “Reftime1” and“Reftime2”. In this case, the delay amounts α and β are different fromeach other.

As a result, the reception side can obtain “PTS1_1” which is a time onthe first time axis having 90 kHz accuracy corresponding to the displaystart time (begin) on the second time axis by the following formula (6)at the time of original broadcasting.PTS1_1=PTS1+(3 sec?1 sec)*90K  (6)

Furthermore, the reception side can obtain “PTS2_1” which is a time onthe first time axis having 90 kHz accuracy corresponding to the displaystart time (begin) on the second time axis by the following formula (7)at the time of rebroadcasting. With this processing, the display timingof the subtitle can be controlled at the time of rebroadcasting,similarly to the time of the original broadcasting.PTS2_1=PTS2+(3 sec?1 sec)*90K  (7)

Note that, in the example in FIG. 8, the subtitle PES packet includingthe TTLM document having the display timing information in which thedisplay start time is “J” and the display end time is “K” is transmittedonly once in the sample period, and the subtitle PES packet includingthe TTLM document having the display timing information in which thedisplay start time is “P” and the display end time is “R” is similarlytransmitted only once in the sample period.

However, to increase the display probability of the subtitle at the timeof random access caused by channel switching, it is considered tosequentially generate the subtitle PES packets including the same TTLMdocument in synchronization with the sample period and sequentiallytransmit the generated packets. In that case, in each subtitle PESpacket, times indicated by the reference time information included inthe subtitle PES packets sequentially change as the corresponding sampleperiod advances.

FIG. 10 is a schematic diagram of an exemplary content (packetstructure) of the subtitle PES packet. All the subtitle PES packetshaving a time stamp A0 (Timestamp A0), a time stamp A1 (Timestamp A1),and a time stamp A2 (Timestamp A2) have the TTLM document with thedisplay timing information in which the display start time is “J” andthe display end time is “K” in the payloads. However, the reference timeinformation included in the subtitle PES packets changes to “Reftime10”,“Reftime11”, and “Reftime12”. In this case, in the subtitle PES packetshaving the time stamps A1 and A2, the display start time “J” is beforethe time indicated in the reference time information. The reception sidecan find that the display start time has already passed.

Furthermore, similarly, all the subtitle PES packets having a time stampB0 (Timestamp B0), a time stamp B1 (Timestamp B1), and a time stamp B2(Timestamp B2) have the TTLM document with the display timinginformation in which the display start time is “P” and the display endtime is “R” in the payloads. However, the reference time informationincluded in the subtitle PES packets changes to “Reftime20”,“Reftime21”, and “Reftime22”. In this case, in the subtitle PES packetshaving the time stamps B1 and B2, the display start time “P” is beforethe time indicated in the reference time information. The reception sidecan find that the display start time has already passed.

Note that, in the above, an example has been described in which thepayload of the subtitle PES packet includes the TTML segment(TTML_segment) and the reference time segment (Reftime_segment)regarding the single subtitle content. However, it is considered toinclude TTML segments and reference time segments regarding a pluralityof subtitle contents which has been individually produced in the payloadof the subtitle PES packet.

That is, one or more pairs (group) of the TTML segments and thereference time segments may be included in the payload of the subtitlePES packet. In consideration of this, as will be described later, ineach pair, the TTML segment and the reference time segment areassociated with each other with identification information“segment_associate_id”.

FIG. 11 illustrates an example of two subtitle contents which have beenindividually produced. For example, a subtitle content S1 issynchronized with a video, and subtitles relating to voices ofrespective characters are displayed by using the subtitle content S1.Furthermore, for example, a subtitle content S2 is not synchronized witha video, and subtitles of explanation of a story or a scene, actorinformation, and other general information (for example, weatherforecasts and the like) are displayed by using the subtitle content S2.

FIG. 12 schematically illustrates an exemplary content (packetstructure) of a subtitle PES packet in a case where the subtitlecontents S1 and S2 exist. A payload of a subtitle PES packet having atime stamp A (Timestamp A) as a PTS includes a TTML segment “S1 TTML”having a TTLM document with display timing information in which adisplay start time regarding the subtitle content S1 is “S1_b1” and adisplay end time is “S1_e1”, and the payload includes a reference timesegment “Reftime A_S1” having reference time information “A_S1”.

Furthermore, in the subtitle PES packet, the payload includes a TTMLsegment “S2 TTML” having a TTLM document with display timing informationin which a display start time regarding the subtitle content S2 is“S2_b1” and a display end time is “S2_e1” and includes a reference timesegment “Reftime A_S2” having reference time information “A_S2”.

Furthermore, a payload of a subtitle PES packet having a time stamp B(Timestamp B) as a PTS includes a TTML segment “S1 TTML” having a TTLMdocument with display timing information in which a display start timeregarding the subtitle content S1 is “S1_b2” and a display end time is“S1_e2”, and the payload includes a reference time segment “ReftimeB_S1” having reference time information “B_S1”.

Furthermore, in the subtitle PES packet, the payload includes a TTMLsegment “S2 TTML” having a TTLM document with display timing informationin which a display start time regarding the subtitle content S2 is“S2_b2” and a display end time is “S2_e2” and includes a reference timesegment “Reftime B_S2” having reference time information “B_S2”.

In addition, a payload of a subtitle PES packet having a time stamp C(Timestamp C) as a PTS includes a TTML segment “S1 TTML” having a TTLMdocument with display timing information in which a display start timeregarding the subtitle content S1 is “S1_b3” and a display end time is“S1_e3”, and the payload includes a reference time segment “ReftimeC_S1” having reference time information “C_S1”.

FIG. 13 is a diagram of an exemplary arrangement sequence in a casewhere TTLM documents and reference time segments regarding the subtitlecontents S1 and 52 exist in the subtitle PES packet. This examplecorresponds to the subtitle PES packet having the time stamp A(Timestamp A) in FIG. 12 as the PTS.

In FIG. 13(a), a reference time segment “Reftime A_S1”, a TTLM document“S1 TTML”, the reference time segment “Reftime A_S2”, and a TTML segment“S2 TTML” are arranged in this sequence. In FIG. 13(b), the referencetime segment “Reftime A_S1”, the reference time segment “Reftime A_S2”,the TTLM document “S1 TTML”, and the TTML segment “S2 TTML” are arrangedin this sequence. These arrangement sequences are merely an example, andother arrangement sequence may be used. Note that the reference timesegment “Reftime A_S1” and the TTLM document “S1 TTML” are associatedwith each other with identification information “segment_associate_id1”,and the reference time segment “Reftime A_S2” and the TTML segment “S2TTML” are associated with each other with “segment_associate_id2”.

Furthermore, as illustrated in FIG. 13(c), a single reference timesegment “Reftime A”, the TTLM document “S1 TTML”, and the TTML segment“S2 TTML” may be arranged. In this case, the single reference timesegment “Reftime A_S” includes a plurality of pieces of associationinformation, and the TTLM document “S1 TTML” is associated with“segment_associate_id1”, and the TTLM document “S2 TTML” is associatedwith “segment_associate_id2”.

FIG. 14 illustrates an exemplary structure of a subtitle PES packet.FIG. 14(a) illustrates a case where data of a single subtitle content isincluded. A PTS is included in a header, and a single pair of areference time segment and a TTML segment exists in a payload. FIG.14(b) is a modification of FIG. 14(a) and is a case where transmissionof reference time information is omitted, and only the TTML segmentexists in the payload.

FIG. 14(c) illustrates a case where data of a plurality of, here, twosubtitle contents are included. The PTS is included in the header, andtwo pairs of the reference time segments and the TTML segments exist inthe payload. FIG. 14(d) illustrates a case where data of a plurality of,here, two subtitle contents are included. The PTS is included in theheader, and a single reference time segment and two TTML segments existin the payload.

FIG. 15(a) illustrates an exemplary structure of a subtitle PES packet(PES_packet). A fixed pattern of “0x000001” is arranged in a 24-bitfield of “PES_startcode_prefix”. An 8-bit field of “stream_id” indicatesa stream identifier. In a case of the subtitle PES packet, “10111101”which is a value indicating “private stream1” is described. A 16-bitfield of “PES_packet_length” indicates the number of subsequent bytes asa length (size) of a PES packet.

After “PES_packet_length”, a field of “Optional_PES_header ( )” exists.In this field, a time stamp such as a PTS and a DTS is arranged. Afterthis field, a field of “PES_packet_data_byte” exists. This fieldcorresponds to a PES payload. In this field, “PES_data_byte_field ( )”for containing data is arranged.

FIG. 15(b) illustrates an exemplary structure of “PES_data_byte_field()”. An 8-bit field of “data_identifier” indicates an identifier foridentifying a kind of data with a container portion. Since theconventional subtitle (in a case of bitmap) is supposed to be indicatedby “0x20”, a text can be identified with a new value, for example,“0x21”.

An 8-bit field of “subtitle_stream_id” indicates an identifier foridentifying a kind of a subtitle stream. In a case of a subtitle streamfor transmitting text information, for example, a new value “0x01” isarranged, and the subtitle stream can be distinguished from aconventional subtitle stream “0x00” for transmitting a bit map.

After the field of “subtitle_stream_id”, a field of“Subtitling_segments( )” exists after a pattern of “00001111”. A segmentpacket is arranged in this field. After this field, an 8-bit field of“end_of_PES_data_field_marker” exists. This field is a marker indicatingthe end of the PES packet.

FIG. 16 illustrates an exemplary definition of a TT subtitle segmenttype (TT_subtitle segment_type). A character string of “0xA0” indicatesa TTML segment (TTML_segment). A character string of “0xA1” indicates areference time segment (Reftime_segment).

FIG. 17(a) illustrates an exemplary structure (Syntax) of the TTMLsegment (TTML_segment). FIG. 17(b) illustrates a content (Semantics) ofmain information in the exemplary structure and the like. An 8-bit fieldof “sync_byte” is a unique word indicating the start of a segment. An8-bit field of “segment_type” indicates a kind of the segment (segmenttype). Here, a character string of “0xA0” indicating that the segment isa TTML segment (TTML_segment) is arranged.

A 16-bit field of “segment_length” indicates the number of subsequentbytes as a length (size) of a subtitle segment. A 4-bit field of“TTML_version_number” indicates an update version of information. In acase where the information is updated, a value is incremented by one. An8-bit field of “segment_associate_id” indicates identificationinformation used for identifying mutually associated segments. In afield of “segment_payload ( )”, a TTML document is arranged.

FIG. 18(a) illustrates an exemplary structure (Syntax) of a referencetime segment (Reftime_segment). FIG. 18(b) illustrates a content(Semantics) of main information in the exemplary structure and the like.An 8-bit field of “sync_byte” is a unique word indicating the start of asegment. An 8-bit field of “segment_type” indicates a kind of thesegment (segment type). Here, a character string of “0xA1” indicatingthe reference time segment (Reftime_segment) is arranged.

A 16-bit field of “segment_length” indicates the number of subsequentbytes as a length (size) of a subtitle segment. A 4-bit field of“reftime_version_number” indicates an update version of information. Ina case where the information is updated, a value is incremented by one.An 8-bit field of “number_of reftime_targets” indicates the number oftargets to which “reftime” is supplied. An 8-bit field of“segment_associate_id” indicates identification information used foridentifying mutually associated segments.

An 8-bit field of “reftime_hour” indicates an hour described in adecimal of the reference time information. An 8-bit field of“reftime_minute” indicates a minute described in a decimal of thereference time information. An 8-bit field of “reftime_second” indicatesa second described in a decimal of the reference time information. An8-bit field of “reftime_frame” indicates a frame described in a decimalof the reference time information.

Returning to FIG. 2, the TS formatter 116 TS-packetizes and multiplexesthe video stream generated by the video encoder 112, the audio streamgenerated by the audio encoder 113, and the subtitle stream generated bythe subtitle encoder 115 to obtain a transport stream TS as amultiplexed stream.

An operation of the stream generation unit 110 illustrated in FIG. 2will be briefly described. The image data DV is supplied to the videoencoder 112. The video encoder 112 encodes the image data DV andgenerates a video stream (PES stream) including a video PES packethaving encoded image data in a payload. The video stream is supplied tothe TS formatter 116.

Furthermore, the audio data DA is supplied to the audio encoder 113. Theaudio encoder 113 encodes the audio data DA and generates an audiostream (PES stream) including an audio PES packet having encoded audiodata. The audio stream is supplied to the TS formatter 116.

Furthermore, the data DT including the text data (character code) as thesubtitle information and display control information of the data issupplied to the text format conversion unit 114. The text formatconversion unit 114 obtains text information of a subtitle in apredetermined format having display timing information, here, a TTML.The TTML is supplied to the subtitle encoder 115.

The subtitle encoder 115 generates a TTML segment (TTML_segment)including a TTML document obtained by the text format conversion unit114. Then, the subtitle encoder 115 generates a subtitle stream (PESstream) including a subtitle PES packet in which the TTML segment isarranged in the payload.

The subtitle encoder 115 generates the subtitle PES packet insynchronization with a sample period and inserts a time stamp (90 kHzaccuracy) on a first time axis indicating a start time of thecorresponding sample period to a header of the subtitle PES packet as aPTS.

Furthermore, the subtitle encoder 115 generates a reference time segment(Reftime_segment) having reference time information (hour-minute-secondframe) of a second time axis regarding a display timing, associated withthe start time of the corresponding sample period, on the basis oftiming management by the control unit 111. Then, the subtitle encoder115 makes the reference time segment (Reftime_segment) be included inthe payload of the subtitle PES packet.

The subtitle stream generated by the subtitle encoder 115 is supplied tothe TS formatter 116. The TS formatter 116 TS-packetizes and multiplexesthe stream generated by each encoder and generates the transport streamTS as a multiplexed stream.

[Exemplary Configuration of Television Receiver]

FIG. 19 illustrates an exemplary configuration of the televisionreceiver 200. The television receiver 200 includes a reception unit 201,a TS analysis unit (demultiplexer) 202, a video decoder 203, a videosuperimposition unit 204, a panel drive circuit 205, and a display panel206. Furthermore, the television receiver 200 includes an audio decoder207, an audio output circuit 208, a speaker 209, and a subtitle decoder210. In addition, the television receiver 200 further includes a CPU221, a flash ROM 222, a DRAM 223, an internal bus 224, a remote controlreception unit 225, and a remote control transmitter 226.

The CPU 221 controls an operation of each unit of the televisionreceiver 200. The flash ROM 222 stores control software and holds data.The DRAM 223 configures a work area of the CPU 221. The CPU 221 developssoftware and data read from the flash ROM 222 on the DRAM 223 toactivate the software and controls each unit of the television receiver200.

The remote control reception unit 225 receives a remote control signal(remote control code) transmitted from the remote control transmitter226 and supplies the signal to the CPU 221. The CPU 221 controls eachunit of the television receiver 200 on the basis of the remote controlcode. The CPU 221, the flash ROM 222, and the DRAM 223 are connected tothe internal bus 224.

The reception unit 201 receives the transport stream TS transmitted fromthe broadcasting transmission system 100 on a broadcast wave. Asdescribed above, the transport stream TS includes a video stream, anaudio stream, and a subtitle stream. The TS analysis unit 202 extractsthe video stream, the audio stream, and the subtitle stream from thetransport stream TS.

The audio decoder 207 decodes an audio PES packet included in the audiostream extracted by the TS analysis unit 202 to obtain audio data. Theaudio output circuit 208 performs necessary processing such as D/Aconversion and amplification on the audio data and supplies the data tothe speaker 209. The video decoder 203 decodes a video PES packetincluded in the video stream extracted by the TS analysis unit 202 toobtain image data.

The subtitle decoder 210 decodes a subtitle PES packet included in thesubtitle stream extracted by the TS analysis unit 202 to obtain bit mapdata of each region (subtitle graphics data) to be superimposed on theimage data. As described above, the payload of the subtitle PES packetincludes the TTML segment including the TTML document (refer to FIGS. 3to 5 and FIG. 17) and the reference time segment having the referencetime information (refer to FIG. 18). The subtitle decoder 210 extractsthe TTML document from the TTML segment and obtains the bit map data ofeach region on the basis of the TTML document.

Furthermore, the subtitle decoder 210 extracts information regarding thedisplay timing (begin, end) of each region from the body of the TTMLdocument (refer to FIG. 5) and transmits the information to the CPU 221.The display timing (begin, end) is only a relative timing for eachpackage of the TTML. The display timing is not synchronized with thesystem and is independent from timing management at the time ofdistribution.

Furthermore, the subtitle decoder 210 extracts the reference timeinformation of the second time axis regarding the display timing of eachregion from the reference time segment and transmits the information tothe CPU 211. Furthermore, the subtitle decoder 210 transmits the timestamp (PTS) on the first time axis with 90 kHz accuracy included in theheader of the subtitle PES packet to the CPU 211. Regarding the timestamp (PTS), timings are uniformly managed in the whole system.

By using the time stamp and the reference time information (start timeof sample period indicated by second time axis), the CPU 211 convertsthe display start time and the display end time of each region indicatedby the information regarding the display timing (begin, end) into a timeon the first time axis with 90 kHz accuracy (refer to formulas (2) and(3) above).

Note that the TTML segments and the reference time segments regardingthe plurality of subtitle contents which has been individually producedmay be included in the payload of the subtitle PES packet. That is, notonly one but also two or more pairs (group) of the TTML segments and thereference time segments may be included in the payload of the subtitlePES packet.

However, as described above, in each pair, the TTML segment and thereference time segment are associated with each other with theidentification information “segment_associate_id”. In a case where theCPU 211 converts a display start time and a display end time of eachregion in a TTML document included in a TTML segment into a time with 90kHz accuracy, the CPU 211 prevents wrong conversion by using thereference time information of the reference time segment associated withthe TTML segment.

The video superimposition unit 204 superimposes the bit map data of eachregion obtained from the subtitle decoder 210 on the image data obtainedby the video decoder 203. In this case, under the control of the CPU211, the video superimposition unit 204 superimposes the bit map data ofeach region only in a period from the display start time to the displayend time with 90 kHz accuracy converted as described above.

Furthermore, to increase the display probability of subtitles at thetime of random access caused by channel switching, a case is consideredwhere the subtitle PES packets including the same TTLM document aresequentially generated and transmitted in synchronization with thesample period (refer to FIG. 10). In that case, the display start timeof each region indicated by the information regarding the display timing(begin) may be positioned before a reference time (start time of sampleperiod) “Reftime” indicated by the reference time information.

When the display start time of each region indicated by the informationregarding the display timing (begin) is positioned before the start timeof the sample period indicated by the reference time information, thevideo superimposition unit 204 immediately superimposes the bit map dataof each region obtained from the subtitle decoder 210 on the image dataobtained by the video decoder 203 under the control of the CPU 211.

A flowchart in FIG. 20 illustrates an exemplary processing procedure ofsubtitle display control performed each time when the CPU 211 receivesthe subtitle PES packet. Note that, in this example, the references “J”and “K” respectively indicates the display start time and the displayend time indicated by the information regarding the display timing(begin, end) (refer to FIG. 10).

In step ST1, the CPU 211 determines whether “Reftime” is smaller than“J”. When “Reftime” is smaller than “J” (for example, “Reftime 10” inFIG. 10), the CPU 211 waits till a system clock corresponds to a timingof “J” and performs control to superimpose the bit map data of eachregion on the image data and to start to display the subtitle at thetiming of “J” in step ST2.

When “Reftime” is not smaller than “J” in step ST1, the CPU 211determines in step ST3 whether “Reftime” is equal to or larger than “J”and equal to or smaller than “K”. When “Reftime” is equal to or largerthan “J” and equal to or smaller than “K” (for example, “Reftime 11” inFIG. 10), the procedure proceeds to step ST4.

In step ST4, the CPU 211 determines whether a time from “Reftime” to “K”is equal to or longer than a threshold TH, that is, whether there is asufficient time from “Reftime” to “K”. When there is a sufficient timeand when the subtitle display has already started and there is enoughtime before the end of the display, the CPU 211, in step ST5,immediately performs control to superimpose the bit map data of eachregion on the image data and to start display of the subtitle.

Furthermore, when the “Reftime” is not equal to or larger than “J” andequal to or smaller than “K” in step ST3, and in addition, when the timefrom “Reftime” to “K” is not equal to or longer than the threshold TH instep ST4, the CPU 211 performs control in step ST6 so as not tosuperimpose the bit map data of each region on the image data, that is,not to display the subtitle.

Returning to FIG. 19, the panel drive circuit 205 drives the displaypanel 206 on the basis of image data for display obtained by the videosuperimposition unit 204. The display panel 206 includes, for example, aLiquid Crystal Display (LCD), an organic electroluminescence (EL)display, and the like.

An operation of the television receiver 200 illustrated in FIG. 19 willbe briefly described. The reception unit 201 receives the transportstream TS transmitted from the broadcasting transmission system 100 on abroadcast wave. The transport stream TS includes a video stream, anaudio stream, and a subtitle stream.

The transport stream TS is supplied to the TS analysis unit 202. The TSanalysis unit 202 extracts the video stream, the audio stream, and thesubtitle stream from the transport stream TS. The video stream (PESstream) extracted by the TS analysis unit 202 is supplied to the videodecoder 203. The video decoder 203 decodes a video PES packet includedin the video stream to obtain image data. The image data is supplied tothe video superimposition unit 204.

Furthermore, the subtitle stream (PES stream) extracted by the TSanalysis unit 202 is supplied to the subtitle decoder 210. The subtitledecoder 210 decodes a subtitle PES packet included in the subtitlestream to obtain bit map data of each region (subtitle graphics data) tobe superimposed on the image data.

In this case, the TTML document is extracted from the TTML segmentincluded in the payload of the subtitle PES packet, and bit map data ofeach region is obtained on the basis of the TTML document.

Furthermore, the subtitle decoder 210 extracts information regarding thedisplay timing (begin, end) of each region from the body of the TTMLdocument (refer to FIG. 5) and transmits the information to the CPU 221.Furthermore, the subtitle decoder 210 extracts the reference timeinformation of the second time axis regarding the display timing of eachregion from the reference time segment and transmits the extractedinformation to the CPU 211. Furthermore, the subtitle decoder 210extracts the time stamp (PTS) on the first time axis with 90 kHzaccuracy included in the header of the subtitle PES packet and transmitsthe time stamp to the CPU 211.

By using the time stamp and the reference time information (start timeof sample period indicated by second time axis), the CPU 211 convertsthe display start time and the display end time of each region indicatedby the information regarding the display timing (begin, end) into a timeon the first time axis with 90 kHz accuracy. (refer to formulas (2) and(3) above).

The bit map data of each region output from the subtitle decoder 210 issupplied to the video superimposition unit 204. The videosuperimposition unit 204 superimposes the bit map data of each regionobtained from the subtitle decoder 210 on the image data obtained by thevideo decoder 203. In this case, under the control of the CPU 211, thevideo superimposition unit 204 superimposes the bit map data of eachregion only in a period from the display start time to the display endtime with 90 kHz accuracy converted as described above.

Note that, in this case, when the display start time of each regionindicated by the information regarding the display timing (begin) ispositioned before the start time of the sample period, the videosuperimposition unit 204 immediately superimposes the bit map data ofeach region obtained from the subtitle decoder 210 on the image dataobtained by the video decoder 203 under the control of the CPU 211.

The image data for display obtained by the video superimposition unit204 is supplied to the panel drive circuit 205. The panel drive circuit205 drives the display panel 206 on the basis of video data for display.With this drive, an image on which the regions are superimposed isdisplayed on the display panel 206.

As described above, in the transmission/reception system 10 illustratedin FIG. 1, the broadcasting transmission system 100 generates andtransmits the subtitle PES packet in synchronization with the sampleperiod, the header of the subtitle PES packet includes the time stamp(PTS) on the first time axis indicating the start time of thecorresponding sample period, and the payload of the subtitle PES packetincludes the reference time information of the second time axisregarding the display timing of each region, associated with the starttime of the corresponding sample period. Therefore, it is possible tosecure an association with the system timing at the time of transmissionwithout changing the display timing in the text information of thesubtitle, and the reception side can display the subtitle at anappropriate timing.

Furthermore, in the transmission/reception system 10 illustrated in FIG.1, the broadcasting transmission system 100 associates the TTML segmentand the reference time segment with each other with the identificationinformation in each pair of the TTML segment and the reference timesegment included in the payload of the subtitle PES packet. Therefore,in a case where the reception side converts a display start time and adisplay end time of each region in a TTML document included in a certainTTML segment into a time with 90 kHz accuracy, wrong conversion can beprevented by using the reference time information of the reference timesegment associated with the TTML segment.

Furthermore, in the transmission/reception system 10 illustrated in FIG.1, the television receiver 200 controls the display timing of thesubtitle according to the text information of the subtitle on the basisof the time stamp (PTS) included in the header of the subtitle PESpacket and the reference time information included in the payload.Therefore, it is possible to display the subtitle at an appropriatetiming.

2. Modification

Note that, in the above embodiment, the reference time informationincluded in the payload of the subtitle PES packet is assumed as timeinformation indicating the start time “Reftime” of the correspondingsample period. However, it can also be considered to use timeinformation indicating the difference “A” (refer to FIG. 7) between thedisplay start time indicated by the display timing information and thestart time of the sample period or a start time of a sample periodcorresponding to the display end time indicated by the display timinginformation.

Furthermore, in the above embodiment, an example has been described inwhich the TTML is used as the text information of the subtitle in apredetermined format having the display timing information. However, thepresent technology is not limited to this, and it is considered to useother timed text information having information equivalent to the TTML.For example, a format derived from the TTML may be used.

Furthermore, in the above embodiment, the transmission/reception system10 including the broadcasting transmission system 100 and the televisionreceiver 200 has been described. However, a configuration of atransmission/reception system to which the present technology can beapplied is not limited to this. For example, a configuration may be usedin which a portion of the television receiver 200 is replaced with a settop box and a monitor connected with a digital interface such as aHigh-Definition Multimedia Interface (HDMI). Note that the “HDMI” is aregistered trademark.

Furthermore, in the above embodiment, an example has been described inwhich the container (multiplexed stream) is a MPEG-2 transport stream.Naturally, the present technology can be similarly applied to a casewhere the multiplexed stream is a MMT stream, a DASH/ISOBMFF stream, orthe like.

Furthermore, the present technology can have a configuration below.

(1) A transmitter including:

a packet transmission unit configured to generate and transmit a packetin which a document of text information of a subtitle having displaytiming information is included in a payload in synchronization with asample period, in which

a time stamp on a first time axis indicating a start time of thecorresponding sample period is included in a header of the packet, and

the payload of the packet further includes reference time information ofa second time axis regarding the display timing, associated with thestart time of the corresponding sample period.

(2) The transmitter according to (1), in which

the reference time information is time information indicating the starttime of the corresponding sample period.

(3) The transmitter according to (1), in which

the reference time information is time information indicating adifference between a display start time indicated by the display timinginformation and the start time of the corresponding sample period or adifference between a display end time indicated by the display timinginformation and the start time of the corresponding sample period.

(4) The transmitter according to any one of (1) to (3), in which

a time is indicated by a count value of 90 kHz on the first time axis,and a time is indicated by an hour-minute-second frame on the secondtime axis.

(5) The transmitter according to any one of (1) to (4), in which

the packet is a PES packet.

(6) The transmitter according to any one of (1) to (5), in which

the payload of the packet includes a first segment having the documentof the text information of the subtitle and a second segment having thereference time information regarding the display timing.

(7) The transmitter according to (6), in which

the first segment is associated with the second segment corresponding tothe first segment with identification information.

(8) The transmitter according to any one of (1) to (7), in which

the packet transmission unit generates and transmits the packet in thesample period after the display start time indicated by the displaytiming information has passed.

(9) A transmission method including:

generating and transmitting a packet in which a document of textinformation of a subtitle having display timing information is includedin a payload in synchronization with a sample period by a transmissionunit, in which

a time stamp on a first time axis indicating a start time of thecorresponding sample period is included in a header of the packet, and

the payload of the packet further includes reference time information ofa second time axis regarding the display timing, associated with thestart time of the corresponding sample period.

(10) A receiver including:

a reception unit configured to receive a packet in which a document oftext information of a subtitle having display timing information isincluded in a payload in synchronization with a sample period, in which

a time stamp on a first time axis indicating a start time of thecorresponding sample period is included in a header of the packet, and

the payload of the packet further includes reference time information ofa second time axis regarding the display timing, associated with thestart time of the corresponding sample period,

the receiver further including:

a control unit configured to control a display timing of the subtitleaccording to the text information of the subtitle on the basis of thetime stamp and the reference time information.

(11) The receiver according to (10), in which

the control unit converts a display start time and a display end timeindicated by the display timing information into a time on the firsttime axis by using the time stamp and the reference time information andcontrols the display timing of the subtitle by using the converted time.

(12) The receiver according to (10) or (11), in which

the control unit performs control to immediately display the subtitleaccording to the text information of the subtitle when the display starttime indicated by the display timing information is positioned beforethe start time of the sample period.

(13) The receiver according to any one of (10) to (12), in which

the payload of the packet includes a first segment having the documentof the text information of the subtitle and a second segment having thereference time information regarding the display timing,

the first segment is associated with the second segment corresponding tothe first segment with identification information, and

the control unit controls the display timing of the subtitle accordingto the text information of the subtitle included in the first segment byusing the reference time information included in the second segmentassociated with the first segment.

(14) A reception method including:

receiving a packet in which a document of text information of a subtitlehaving display timing information is included in a payload insynchronization with a sample period by a reception unit, in which

a time stamp on a first time axis indicating a start time of thecorresponding sample period is included in a header of the packet,

the payload of the packet further includes reference time information ofa second time axis regarding the display timing, associated with thestart time of the corresponding sample period, and

the reception unit controls a display timing of the subtitle accordingto the text information of the subtitle on the basis of the time stampand the reference time information.

The main feature of the present technology is that an association with asystem timing at the time of transmission is secured without changingthe display timing in the text information of the subtitle and that thereception side can display the subtitle at an appropriate timing bygenerating and transmitting the subtitle PES packet in synchronizationwith the sample period, including the time stamp (PTS) on the first timeaxis indicating the start time of the corresponding sample period in theheader, and including the reference time information of the second timeaxis regarding the display timing of each region, associated with thestart time of the corresponding sample period in the payload (refer toFIGS. 7 and 8).

REFERENCE SIGNS LIST

-   10 Transmission/reception system-   100 Broadcast transmission system-   110 Stream generation unit-   111 Control unit-   112 Video encoder-   113 Audio encoder-   114 Text format conversion unit-   115 Subtitle encoder-   116 TS formatter-   200 Television receiver-   201 Reception unit-   202 TS analysis unit-   203 Video decoder-   204 Video superimposition unit-   205 Panel drive circuit-   206 Display panel-   207 Audio decoder-   208 Audio output circuit-   209 Speaker-   210 Subtitle decoder-   221 CPU-   222 Flash ROM-   223 DRAM-   224 Internal bus-   225 Remote control reception unit-   226 Remote control transmitter

The invention claimed is:
 1. A transmitter comprising: processingcircuitry configured to generate and transmit a packet in which adocument of text information of a subtitle having display timinginformation is included in a payload in synchronization with acorresponding sample period, wherein a time stamp indicating a starttime of the corresponding sample period on a first time axis is includedin a header of the packet, and the payload of the packet furtherincludes reference time information corresponding to the start time ofthe corresponding sample period indicated in the time stamp of theheader of the packet, the reference time information being on a secondtime axis that uses a reference point different than the reference pointof the first time axis of the time stamp of the header of the packet,the reference time information being different from the display timinginformation of the subtitle.
 2. The transmitter according to claim 1,wherein the reference time information is time information indicating adifference between a display start time indicated by the display timinginformation and the start time of the corresponding sample period or adifference between a display end time indicated by the display timinginformation and the start time of the corresponding sample period. 3.The transmitter according to claim 1, wherein a time is indicated by acount value of 90 kHz on the first time axis, and a time is indicated byan hour-minute-second frame on the second time axis.
 4. The transmitteraccording to claim 1, wherein the packet is a packetized elementarystream (PES) packet.
 5. The transmitter according to claim 1, whereinthe payload of the packet includes a first segment having the documentof the text information of the subtitle and a second segment having thereference time information.
 6. The transmitter according to claim 5,wherein the first segment is associated with the second segment.
 7. Thetransmitter according to claim 1, wherein the processing circuitry isconfigured to generate and transmit the packet in the correspondingsample period after a display start time indicated by the display timinginformation has passed.
 8. A transmission method comprising: generatingand transmitting a packet in which a document of text information of asubtitle having display timing information is included in a payload insynchronization with a corresponding sample period by a transmissionunit, wherein a time stamp indicating a start time of the correspondingsample period on a first time axis is included in a header of thepacket, and the payload of the packet further includes reference timeinformation corresponding to the start time of the corresponding sampleperiod indicated in the time stamp of the header of the packet, thereference time information being on a second time axis that uses areference point different than the reference point of the first timeaxis of the time stamp of the header of the packet, the reference timeinformation being different from the display timing information of thesubtitle.
 9. A receiver comprising: processing circuitry configured toreceive a packet in which a document of text information of a subtitlehaving display timing information is included in a payload insynchronization with a corresponding sample period, wherein a time stampindicating a start time of the corresponding sample period on a firsttime axis is included in a header of the packet, and the payload of thepacket further includes reference time information corresponding to thestart time of the corresponding sample period indicated in the timestamp of the header of the packet, the reference time information beingon a second time axis that uses a reference point different than thereference point of the first time axis of the time stamp of the headerof the packet, the reference time information being different from thedisplay timing information of the subtitle, the processing circuitry isfurther configured to control a display timing of the subtitle accordingto the text information of the subtitle on the basis of the time stampand the reference time information.
 10. The receiver according to claim9, wherein the processing circuitry is configured to convert a displaystart time and a display end time indicated by the display timinginformation into a time on the first time axis by using the time stampand the reference time information and is configured to control thedisplay timing of the subtitle by using the converted display start timeand the converted display end time on the first time axis.
 11. Thereceiver according to claim 9, wherein the processing circuitry isconfigured to perform control to immediately display the subtitleaccording to the text information of the subtitle when a display starttime indicated by the display timing information is positioned beforethe start time of the corresponding sample period.
 12. The receiveraccording to claim 9, wherein the payload of the packet includes a firstsegment having the document of the text information of the subtitle anda second segment having the reference time information, the firstsegment is associated with the second segment, and the processingcircuitry is configured to control the display timing of the subtitleaccording to the text information of the subtitle included in the firstsegment by using the reference time information included in the secondsegment associated with the first segment.
 13. A reception methodcomprising: receiving, by processing circuitry of a receiver apparatus,a packet in which a document of text information of a subtitle havingdisplay timing information is included in a payload in synchronizationwith a corresponding sample period by a reception unit, wherein a timestamp indicating a start time of the corresponding sample period on afirst time axis is included in a header of the packet, the payload ofthe packet further includes reference time information corresponding tothe start time of the corresponding sample period indicated in the timestamp of the header of the packet, the reference time information beingon a second time axis that uses a reference point different than thereference point of the first time axis of the time stamp of the headerof the packet, the reference time information being different from thedisplay timing information of the subtitle, and the method furtherincludes controlling, by the processing circuitry of the receiverapparatus, a display timing of the subtitle according to the textinformation of the subtitle on the basis of the time stamp and thereference time information.
 14. The transmitter according to claim 1,wherein the time stamp included in the header of the packet is aPresentation Time Stamp (PTS) indicating the start time of thecorresponding sample period on a system time axis as the first timeaxis, and the display timing information of the text information of thesubtitle is on the second time axis and is expressed with respect to thereference point that is the same as the reference point of the referencetime information.
 15. The transmission method according to claim 8,wherein the time stamp included in the header of the packet is aPresentation Time Stamp (PTS) indicating the start time of thecorresponding sample period on a system time axis as the first timeaxis, and the display timing information of the text information of thesubtitle is on the second time axis and is expressed with respect to thereference point that is the same as the reference point of the referencetime information.
 16. The receiver according to claim 9, wherein thetime stamp included in the header of the packet is a Presentation TimeStamp (PTS) indicating the start time of the corresponding sample periodon, a system time axis as the first time axis, and the display timinginformation of the text information of the subtitle is on the secondtime axis and is expressed with respect to the reference point that isthe same as the reference point of the reference time information. 17.The reception method according to claim 13, wherein the time stampincluded in the header of the packet is a Presentation Time Stamp (PTS)indicating the start time of the corresponding sample period on a systemtime axis as the first time axis, and the display timing information ofthe text information of the subtitle is on the second time axis and isexpressed with respect to the reference point that is the same as thereference point of the reference time information.